Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface, showing our new design.

The outermost broken lines illustrate a display screen or portion thereof, and the outermost broken lines form no part of the claimed design. The remaining broken lines illustrate portions of the graphical user interface, and the remaining broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 